Add a non-GOV.UK banner option for email branding

Added an extra name, 'org_banner', for branding types into branding_type table
Added org banner into user model in database
Added checks for new branding type to ensure that the correct data is passed into the dict
Tested new checks in html email options

migrations/versions/0120_add_org_banner_branding.py

@@ -0,0 +1,22 @@
+"""
+
+Revision ID: 0120_add_org_banner_branding
+Revises: 0119_add_email_reply_to
+Create Date: 2017-09-18 14:18:49.087143
+
+"""
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects import postgresql
+
+revision = '0120_add_org_banner_branding'
+down_revision = '0119_add_email_reply_to'
+
+
+def upgrade():
+    op.execute("INSERT INTO branding_type VALUES ('org_banner')")
+
+def downgrade():
+    op.execute("UPDATE services SET branding = 'org' WHERE branding = 'org_banner'")
+    op.execute("DELETE FROM branding_type WHERE name = 'org_banner'")
+